Theme 2-24-Estimates of the outflux of groundwater along the perimeter of coastal aquifers

Abstract

Mauritius is a volcanic basaltic island, located off the east coast of the Republic of Malagasy. The island harnesses both surface water sources and groundwater sources to cater for its water demand. Since the water storage capacity of the water network is poor, the island is often faced with major water stress problems during drought conditions. Increasing the water storage capacity is financially too demanding for the island. However, an alternative option is to optimise the exploitation of the existing water resource. Presently groundwater sources contribute up to 50% domestic water supply, and in some parts of the island, groundwater is the only source of domestic water supply. From past hydrogeological studies carried out over the island, it is known that the aquifers of the island are all unconfined and coastal in nature. Hence overexploitation of the groundwater sources may have serious adverse impacts, such as inducing salt water into the groundwater bodies, and hence polluting this valuable water resource. It is also known that the basement of these coastal aquifers slope downwards towards the sea, and since along the coastal regions there is not geological barriers which can act as retaining walls to the groundwater, significant losses of groundwater takes place along the coast. Past hydrogeological studies, Huntings’ (1973) and SIGMA & SOGREAH (1980) do give a rough indicate of an average rate characteristing the potential groundwater losses to the sea for the whole island. An average value for the whole island is too approximate to be used in studies involving estimates of the potential of aquifers. So far there has not been any study carried out to illustrate the variation of these groundwater loss rates along the coasts of the island. The present study has been undertaken with the objective of highlighting the magnitude and direction of the outflux of groundwater into the sea.